Lacerations and other wounds which compromise the integrity of the skin are common enough that most people have experienced them, from the mundane, such as a skinned knee, to the life-threatening, such as a stab wound or a serious burn. Many breaks to the skin raise the possibility of disfigurement through scarring.
The development of scar tissue is a defensive response to an injury in that it repairs a breach in the skin, eliminating a site of potential infection and reinjury. However, the rampant formation of scar tissue can result in a tough dermal surface lacking the color or consistency of the surrounding skin. Because the flexibility and elasticity of scar tissue differs from that of natural skin, scar tissue can ultimately limit the lives of those who are affected. Scar tissue is generally tougher than the skin tissue in the surrounding area. This is especially true of scar tissue where the skin is subjected to deformation and elastic stresses, such as on or behind the knee or elbow. Such areas can be subject to tear at the skin/scar tissue border. Scar tissue, particularly new scars, covering areas having natural grooves to facilitate bending, such as the lines on the palms of the hands, are often weak at these flex lines. Stretching caused by opening and closing the hand can rupture the scar tissue at these natural grooves, resulting in an accumulation of scar tissue on either side of the groove, causing newly formed tissue in the groove even to have even greater susceptibility to tearing with hand motion. In general, the natural topography of a wound site can increase the likelihood of retearing, resulting in long healing times.
The lack of flexibility and suppleness of scar tissue is complicated by the fact that scarred areas can become naturally contracted during and after formation as the scar becomes thick, leathery, and inelastic. As a result, the motion of those who have extensive skin injury, such as burn victims, can be severely restricted. A severely burned hand can become frozen in a grasp. Scar tissue due to burns around the waist can prevent torsional motions that most people take for granted.
Some preparations for treating wounds are formulated to have a positive effect on the properties of the scar tissue formed during healing. For example, some wound dressings have functions such as reducing wound drying and preventing ultraviolet light exposure. Such formulations can prevent repeated cracking and drying, resulting in, among other things, the formation of scar tissue having improved flexibility, elasticity and color characteristics relative to scar tissue formed in the absence of the formulation.
Some formulations are made of strictly organic materials, such as gels. Gels have properties which make them suitable as wound dressings. They can cool wounds by contacting them directly, yet keep them free from contamination. Another useful property of gels is their consistency: many gels are similar to skin in elasticity and deformability, and they can bend, bunch and stretch with the skin and tissue surfaces to which they are attached without causing tearing or stress at the site of the healing wound.
However, gels can dry out rapidly with time, break down structurally and/or chemically, and they generally must be reapplied, which can be a painful process for the patient, especially if the consistency of the dressing has become stiff due to drying. Some gels can absorb moisture, developing a soft or liquid consistency. Once the gel consistency has been compromised, the potential for bacterial infection increases.
Siloxane gels have been found to be generally superior to other types of gel products in the treatment of wounds and scar tissue. Siloxane gels function by forming a silicone-based polymer matrix over a wound site. Polymer precursors, such as dimethicone, dimethicone crosspolymer, and other siloxanes, are contained in a spreadable preparation which is applied to a wound site. Some polymer precursor formulations include fumed silica. The preparation also contains a volatile component which begins to evaporate upon the application of the preparation to a wound site. The polymer matrix begins to form upon the evaporation of volatile compounds from the spreadable preparation. The preparations are, in many cases, thixotropic, particularly if the formulation contains fumed silica. Thixotropic formulations change from a stiff consistency to a fluid-like consistency upon the application of stress, such as application to a wound, and revert to a stiffer, less fluid consistency once the stress is removed. This property gives siloxane gel precursor formulations the ability to spread easily into a relatively thin layer over a wound and remain in place without oozing away from the wound site, all with a minimum of stress and shear at the wound site.
Another advantage of siloxane gels is that some have been shown to have a beneficial effect on the properties of scar tissue as it is being formed, diminishing the degree of scarring and improving the texture of scar tissue that does form, such that the ultimate appearance of the healed wound is more like surrounding skin. For instance, some siloxane preparations, when applied to developing or newly formed scar tissue, have demonstrated the ability to cause excellent fading, and even near disappearance of the scar with constant application.
Unlike other spreadable preparations on the market for aiding in the healing of wounds, once a degree of polymerization has taken place to form the siloxane polymer matrix, the resultant gel generally has the ability to retain its consistency over time. Furthermore, the unapplied product can be easier to store and use than other types of gels because it can be applied as siloxane polymer matrix precursors which do not “set” until after application.
Because siloxane gels have such beneficial effects upon developing scar tissue, it is desirable that such a preparation also have the ability to include additives which impart additional useful functions to the gel. For example, while the foregoing silicone-based formulations demonstrate superior scar reduction properties, developing scar tissue is susceptible to change in color and/or texture, as well as other types of damage, such as thermal damage, upon exposure to ultraviolet and other wavelengths of radiation. It is thus desirable to incorporate sun screening compounds into the formulation which will be retained upon matrix formation. Furthermore, burns and other injuries which are best served by the topical application of gels can continue to be very painful, even after the wound has begun to scar over. However, the application of the matrix forming preparation can prevent the topical application of pain relievers: unlike bandage-type coverings, most topical gels cannot be simply lifted and resituated. It can thus desirable that matrix forming preparations comprise at least one pain alleviating compound.
Unfortunately, the use of siloxane matrix precursors has severely limited the variety of additives which can be included in silicone wound dressings. Many desirable additives are not readily solvated in the mix of matrix precursors, such as dimethicone and other siloxanes which comprise the spreadable preparation. For example, many effective and commonly used sunscreen additives, such as, for example, Octocrylene, Octinoxate, Octisalate and Oxybenzone may not sufficiently dissolve in the pre-polymerized preparation. Other examples of desirable additives having poor solubility in the pre-polymerization preparation include cortisone-type compounds which reduce pain and inflammation, such as, for example, Hydrocortisone acetate.
A method exploiting the advantages of siloxane matrix-forming wound preparations, yet allowing the inclusion of otherwise insoluble additives in silicone wound dressing formulations would be welcomed as a significant advance in the art of wound dressing preparation.